Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$30.51	5.751%	$32.2646	$32.26	$32.25	$32.30
Purchase #2	$236.70	13.420%	$268.4651	$268.47	$268.45	$268.50
Purchase #3	$107.37	13.543%	$121.9111	$121.91	$121.90	$121.90
Purchase #4	$168.48	6.497%	$179.4261	$179.43	$179.45	$179.40
Purchase #5	$139.76	4.476%	$146.0157	$146.02	$146.00	$146.00
Purchase #6	$40.48	11.375%	$45.0846	$45.08	$45.10	$45.10
Purchase #7	$74.42	3.814%	$77.2584	$77.26	$77.25	$77.30
7 purchase totals =	$797.72		$870.4256	$870.43	$870.40	$870.50